I came from core French too, and was also very stressed out about it. But I was just fine! I understood everything that the profs were saying. They speak relatively slowly, and they are more than happy to stop and explain a word or phrase if you don't understand.
I was concerned that I wasn't fluent enough, so I went to see my prof to talk to her about it, and she actually set me up with a masters student and for $20, we would have conversations for an hour every week. I found that really helpful. All of the French profs I've had so far have been really nice, and very helpful. I doubt you'll struggle understanding, but if you do, don't be afraid to talk to your prof about it!